1. Field of the Invention
This invention relates to speed limiting accessory drive systems and apparatus therefor and more particularly to speed-responsive mechanisms for the transmission of torque and diversion of excess energy in speed-limiting accessory drive systems utilized with prime movers such as liquid cooled internal combustion engines.
Modern day car and truck engines are loaded with a cluster of belt-driven accessories including water pumps, fans, air conditioning compressors, air compressors, power steering pumps, alternators, and exhaust gas recirculation pumps. Increasing consumer usage of such accessories on the one hand, and the fact that the accessories must give sufficient output at both engine idling and highway cruising speeds on the other hand, requires a wide, yet economical, performance range for the complete accessory drive system. In conventional drive systems, accessories are driven at speeds proportional to the engine speed and demand a sizeable portion of the engine's power output. Accordingly, accessories to be used in conventional systems must be designed to give sufficient accessory output at low engine speed yet be able to withstand high rotational speeds without prematurely deteriorating and even bursting. With the present invention, smaller capacity accessories can be utilized to give equivalent or better performance than that obtained with present drive systems and present accessories. By operating accessories through a drive system which limits the maximum accessory speed and therefore limits the torque to a value below that that would have been normally required to drive the accessories above that maximum accessory speed, the economical and functional performance of the engine is less penalized. If the accessory speed is not limited, then during high speed engine operation the majority of the accessories produce excessive output and require excessive drive torque which respectively compromises useful accessory life and represents a continuous power loss of several horsepower to the engine. This power loss appears in the form of reduced engine performance coupled with increased fuel consumption and increased wear in the accessories and accessory drive system.
A preferred relation between the speed of the driving engine and the accessories is to build up the accessory speed at a high rate during lower engine speeds but to limit the accessory speed to a maximum control level when the engine speed exceeds that level. In this manner, sufficient drive is assured for accessory operation at low engine speeds as well as at cruising speeds, yet the accessory drive system which limits accessory speed diverts the excessive engine-delivered energy to the engine's cooling system rather than passing it to the accessories.
Prior attempts to improve the relationship between the engine speed and the accessory speed employing such devices as multi-speed transmissions or infinitely variable transmissions between the engine and accessories have not proven commercially acceptable. Inherent performance deficiencies and cost penalties have made these devices commercially unfeasible. Certain accessory drive systems known in the art have utilized torque transmission mechanisms in which centrifugal weights effect frictional disengagement, however, specific problems such as excessive noise and wear in the clutch facing have prevented their broad commercial implementation. Some air cooled accessory drive mechanisms known in the art require costly heat exchangers which are difficult to manufacture and result in insufficient air circulation. Moreover, providing air-cooled devices with a fan blade heat exchanger resulted in wasted energy, thus further lowering overall engine performance. Because many prior art devices required accommodation for friction pad wear and did not have direct and substantially complete bearing journalling support provided by and between the driven and driving members, complex bearing arrangements were necessary, resulting in increased overall costs. Devices of the prior art typifying the foregoing problems are illustrated in the following patents: U.S. Pat. Nos. 1,365,733; 2,746,587; 2,758,689; 3,081,856; 3,747,731.
The present invention has as one of its more important objects, the provision of a speed-limiting accessory drive system in which the accessory speed is increased by a high drive ratio at lower engine speeds and then limited at a maximum control speed regardless of increased engine speeds beyond that control speed.
This invention has as another object the provision of a speed-limiting accessory drive system in which heat dissipation, lubrication, and noise suppression are provided by circulation of presently available liquid coolants from a liquid cooled internal combustion engine throughout the speed-responsive, torque-transmitting mechanism of the drive system.
A further object of this invention is the provision of speed-limiting accessory drive system utilizing a speed-responsive, torque-transmitting mechanism which avoids the deliverance of excessive engine-delivered energy to the accessories and permits reduced design capacity for the accessory equipment.
A still further object of this invention is the provision of a self-journalling speed-responsive mechanism in an accessory drive system wherein the driven member is substantially completely journalled for bearing support by the driving member thereby eliminating the need for complex bearing arrangements.
Still another object of this invention is the provision of a speed-limiting accessory drive system which reduces the rotary torque necessary to drive the accessories and thereby increases overall engine performance.
Another object of this invention is the provision of an accessory drive system wherein at engine cranking speeds, the associated accessories are disengaged thereby reducing the torque required to start and turn over the engine.